In situ annealing enhancement of the optical properties and laser device performance of InAs quantum dots grown on Si substrates.

The addition of elevated temperature steps (annealing) during the growth of InAs/GaAs quantum dot (QD) structures on Si substrates results in significant improvements in their structural and optical properties and laser device performance. This is shown to result from an increased efficacy of the dislocation filter layers (DFLs); reducing the density of dislocations that arise at the Si/III-V interface which reach the active region. The addition of two annealing steps gives a greater than three reduction in the room temperature threshold current of a 1.3 µm emitting QD laser on Si. The active region of structures grown on Si have a room temperature residual tensile strain of 0.17%, consistent with cool down from the growth temperature and the different Si and GaAs thermal expansion coefficients. This strain limits the amount of III-V material that can be grown before relaxation occurs.

InAsP quantum dot lasers grown by MOVPE.

We report on InAsP quantum dot lasers grown by MOVPE for 730-780 nm wavelength emission and compare performance with InP dot samples grown under similar conditions and with similar structures. 1-4 mm long, uncoated facet InAsP dot lasers emit between 760 and 775 nm and 2 mm long lasers with uncoated facets have threshold current density of 260 Acm(-2), compared with 150 Acm(-2) for InP quantum dot samples, which emit at shorter wavelengths, 715-725 nm. Pulsed lasing is demonstrated for InAsP dots up to 380 K with up to 200 mW output power. Measured absorption spectra indicate the addition of Arsenic to the dots has shifted the available transitions to longer wavelengths but also results in a much larger degree of spectral broadening. These spectra and transmission electron microscopy images indicate that the InAsP dots have a much larger degree of inhomogeneous broadening due to dot size variation, both from layer to layer and within a layer.

Radiative recombination rate measurement by the optically pumped variable stripe length method.

Using the optically pumped variable stripe length technique we demonstrate that, through calibration of measured spontaneous emission spectra, it is possible to determine the total radiative recombination rate for a gain material as a function of the intrinsic quasi-Fermi level separation. Specifically we compare the room temperature optical characteristics of a self-assembled InP/GaInP quantum dot material measured using both optical and electrical pumping. The comparison reveals good agreement between gain and emission spectra measured with the two techniques, for the same inversion, from which we conclude that the carrier distributions in each case are equivalent. The results demonstrate that the optically pumped experiment can provide a good measure of the overall radiative efficiency.